Three Phase Breaker

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VIC1958

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Never seen this before and need to know if it is a violation.
Single phase furnace connected to a three phase breaker. If allowed would it mater which phases the equipment is connected too?
 
VIC1958 said:
Never seen this before and need to know if it is a violation.
Single phase furnace connected to a three phase breaker. If allowed would it mater which phases the equipment is connected too?
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I've seen this quite a bit. We have many three phase breakers that feed 480v , 2 leg lighting circuits. As far as I know it's allowed.
 
No violation. No problem unless its a 240 delta high-leg system in which case one would need to be careful as to phase.
 
augie47 said:
No violation. No problem unless its a 240 delta high-leg system in which case one would need to be careful as to phase.
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Maybe not. If the load is only connected line to line (no neutral) the 3 pole breaker would already be straight rated as opposed to slash rated and you could use any 2 poles to feed the load.
 
VIC1958 said:
It is line to line with no neutral, the rest of what you are saying I do not understand.
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Straight rated means it is rated for 240V between any two phases, or any phase and ground. It is rated for any way you can connect 240V in the system, or whatever its rating may be.

Slash rated means it is rated for example, 120/240V, and both those numbers are important ratings. It is rated 240V between any two phases, but the voltage between any phase and ground cannot exceed 120V. Good for most applications, but problematic if it connects to the high leg in a 120/240V delta system, where the high leg b-phase is 208V phase to ground.
 
Carultch said:
Straight rated means it is rated for 240V between any two phases, or any phase and ground. It is rated for any way you can connect 240V in the system, or whatever its rating may be.

Slash rated means it is rated for example, 120/240V, and both those numbers are important ratings. It is rated 240V between any two phases, but the voltage between any phase and ground cannot exceed 120V. Good for most applications, but problematic if it connects to the high leg in a 120/240V delta system, where the high leg b-phase is 208V phase to ground.
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What would be problematic about it?

JAP>
 
I believe most if not all current production 240 volt "miniature"(add) three pole breakers are straight 240 volt rated. 2 pole breakers is where you need to watch for 120/240 vs straight 240 rating when using a high leg or corner grounded system.
 
GoldDigger said:
Mostly the fact that the slash rated breaker has a maximum line to ground voltage (nominal) of 120V and connecting one of its poles to the high leg exposes it to 208V to ground. :)
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Still don't make sense.
When would one ever use the wild leg and a neutral to feed anything other than a subpanel?

JAP>
 
or should I say when would someone only use the wild leg and a neutral other than for a sub feed?

Never.

JAP>
 
don_resqcapt19 said:
The the energy that the breaker has to interrupt is higher when the ground fault is 208 volts to ground as compared to 120 to ground.
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Does that mean that a 120/240 slash rated breaker could be used at 208V to ground with a reduced AIC rating? I mean physics-wise, not listing-wise.

Cheers, Wayne
 
jap said:
Still don't make sense.
When would one ever use the wild leg and a neutral to feed anything other than a subpanel?

JAP>
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In the case of the two-pole breaker, it is not about using the wild leg-to-neutral, it is about using the wild leg to one of the "tame legs", for 240 Volt single phase loads.

In order to use wild leg-to-neutral, you would need a straight rated 240V single pole breaker, good luck finding one. Either that, or a 277/480V panelboard re-purposed for the system. I can't think of a specific application where you would do this. However, just as a theoretical question, if you do satisfy all voltage requirements of all breakers, is possible/permissible to use the high leg for a 208V single phase-to-neutral load?
 
wwhitney said:
Does that mean that a 120/240 slash rated breaker could be used at 208V to ground with a reduced AIC rating? I mean physics-wise, not listing-wise.

Cheers, Wayne
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Maybe, but you would have to get the AHJ to sign off on the code violation.
 
wwhitney said:
Does that mean that a 120/240 slash rated breaker could be used at 208V to ground with a reduced AIC rating? I mean physics-wise, not listing-wise.

Cheers, Wayne
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I kind of wondered the same thing. Seems like the main thing is how much energy may flow during a fault, and you could easily have a open delta system that has pretty limited capacity on the high leg transformer, yet have a 167 kVA single phase transformer that has much higher fault current though it is only 120 volts to ground.

I think they just made a one size fits all rule more then anything.
 
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